This invention relates generally to apparatus for accurately measuring forces or weights and, more particularly, to a load cell utilizing a force-sensitive vibrating beam resonator for sensing the strain induced in the load cell structure by an applied force.
Conventional load cells used to measure forces or weights of the kind used in weighing scales, for example, employ strain gages or other strain-sensing means such as a variable capacitor, a variable inductance, or optical means for sensing the strain induced in the load cell structure by the applied force. Among the disadvantages of such known load cells is their inherently analog output which requires an analog-to-digital (A/D) conversion to make the load cell compatible with digital electronics which conversion, in turn, causes an additional loss of accuracy and increased cost of manufacture. Additionally, because of the plastic behavior of the epoxy currently used to bond the strain gage to the straining portion of the load cell, creep and hysterisis errors are introduced. Also, the relatively high strain and attendant high stress levels required for strain gages to function properly further contributes to creep and hysterisis errors.
A primary object of the present invention is to provide an improved load cell that overcomes the foregoing disadvantages of currently available load cells.
A more specific object of the invention is to provide a load cell utilizing a crystal resonator in a strain-sensing configuration that directly produces a digital output signal, that has high resolution and accuracy, has a low sensitivity to temperature and exhibits low hysterisis and creep errors.